Mode= Economy Mode merely changes the shift points-- keeping the engine at lower RPM for better MPG.
It will have no affect on your issue.
Sorry, I don't know where the throttle position switch is on your particular chassis. But, if the left window goes to exactly the same gear as when you turn on the exhaust brake, that is a possibility.
One other point-- you mentioned using the exhaust brake in inclement weather. NOT recommended as a 4 wheel "power drift" in an RV is not a pretty sight. Use service brakes to stop in slippery conditions-- that uses all 4 wheels, not just two. Exception may be very long grades, and if used here in slippery conditions, go REALLY slowly.
